The invention pertains to a polishing pad that can be used for the polishing of a substrate, as well as a method of using the polishing pad to polish a substrate.
A semiconductor wafer typically includes a substrate, such as a silicon or gallium arsenide wafer, on which a plurality of integrated circuits have been formed. Integrated circuits are chemically and physically integrated into a substrate by patterning regions in the substrate and layers on the substrate. The layers are generally formed of materials having either a conductive, insulating, or semiconducting nature. It is crucial that the surface onto which the layers are placed is as flat as possible. If a wafer is not flat and smooth, various problems can occur that may result in an inoperable device. Specifically, a smooth topography is desirable because it is difficult to lithographically image and pattern layers applied to rough surfaces. For example, in fabricating integrated circuits, it is necessary to form conductive lines or similar structures above a previously formed structure. However, prior surface formation often leaves the top surface topography of a wafer highly irregular and containing bumps, areas of unequal elevation, troughs, trenches, and other types of surface irregularities. The semiconductor industry continues to concentrate on achieving a surface of even topography by decreasing the number and size of surface imperfections through improved polishing techniques.
Although several surface polishing techniques exist to ensure wafer surface planarity, processes employing chemical-mechanical polishing (also referred to as planarization) techniques have achieved widespread usage during the various stages of integrated circuit fabrication to improve yield, performance, and reliability. A chemical-mechanical polishing (CMP) process typically involves the circular motion of a substrate to be polished (such as a wafer) under a controlled downward pressure relative to a polishing pad that is saturated with a polishing composition (also referred to as a polishing slurry) under controlled conditions.
The polishing composition generally contains small, abrasive particles that mechanically abrade the surface of the substrate to be polished in a mixture with chemicals that chemically react with (e.g., remove and/or oxidize) the surface of the substrate to be polished. Thus, when the polishing pad and the substrate to be polished move with respect to each other, material is removed from the surface of the substrate mechanically by the abrasive particles and chemically by other components in the polishing composition.
Typical polishing pads available for polishing applications, such as CMP processes, are manufactured using both soft and rigid pad materials, which include polymer-impregnated fabrics, microporous films, cellular polymer foams, non-porous polymer sheets, and sintered thermoplastic particles. A pad containing a polyurethane resin impregnated into a polyester non-woven fabric is illustrative of a polymer-impregnated fabric polishing pad. Such polymer-impregnated fabrics are commonly manufactured by impregnating a continuous roll of fabric with a polymer (i.e., generally polyurethane), curing the polymer, and cutting, slicing, and buffing the pad to the desired thickness and lateral dimensions. Microporous polishing pads include microporous urethane films coated onto a base material, which is often an impregnated pad. Such porous films commonly are composed of a series of vertically oriented closed end cylindrical pores. Cellular polymer foam polishing pads contain a closed cell structure that is randomly and uniformly distributed in all three dimensions. The porosity of closed cell polymer foams is typically discontinuous. Non-porous polymer sheet polishing pads include a polishing surface made from solid polymer sheets, which have no intrinsic ability to transport slurry particles (see, for example, U.S. Pat. No. 5,489,233). These solid polishing pads are externally modified with large and small grooves that are cut into the surface of the pad purportedly to provide channels for the passage of slurry during chemical-mechanical polishing. A similar non-porous polymer sheet polishing pad is disclosed in U.S. Pat. No. 6,203,407, wherein the polishing surface of the polishing pad comprises grooves that are oriented in such a way that purportedly improves selectivity in the chemical-mechanical polishing. Also in a similar fashion, U.S. Pat. Nos. 6,022,268, 6,217,434, and 6,287,185 disclose hydrophilic polishing pads with no intrinsic ability to absorb or transport slurry particles. The polishing surface purportedly has a random surface topography including microaspersities that are 10 xcexcm or less and formed by solidifying the polishing surface and macrodefects (or macrotextures) that are 25 xcexcm or greater and formed by cutting. Sintered polishing pads comprising a porous open-celled structure can be prepared from thermoplastic polymer resins. For example, U.S. Pat. Nos. 6,062,968 and 6,126,532 disclose polishing pads with open-celled, microporous substrates, produced by sintering thermoplastic resins with a pellet size of about 50 to about 200 mesh. The resulting polishing pads preferably have a void volume between 25 and 50% and a density of 0.7 to 0.9 g/cm3. Similarly, U.S. Pat. Nos. 6,017,265, 6,106,754, and 6,231,434 disclose polishing pads with uniform, continuously interconnected pore structures, produced by sintering thermoplastic polymers at high pressures in excess of 689.5 kPa (100 psi) in a mold having the desired final pad dimensions.
Where enhanced polishing composition transport is desired on or through a polishing pad, the polishing pad typically is textured with channels, grooves, and/or perforations to improve lateral polishing composition transport during substrate polishing.
Polishing composition delivery and distribution to the polishing surface is important for a CMP process to provide effective substrate planarization. Inadequate or non-uniform polishing composition flow across the polishing pad may give rise to non-uniform polishing rates, poor surface quality across the substrate, or deterioration of the polishing pad. U.S. Pat. No. 5,489,233 discloses the use of large and small flow channels to permit transport of a polishing composition across the surface of a solid polishing pad. U.S. Pat. No. 5,533,923 discloses a polishing pad constructed to include conduits that pass through at least a portion of the polishing pad to permit flow of the polishing composition. Similarly, U.S. Pat. No. 5,554,064 describes a polishing pad containing spaced apart holes to distribute the polishing composition across the pad surface. Alternatively, U.S. Pat. No. 5,562,530 discloses a pulsed-forced system that allows for the down force holding a wafer onto a polishing pad to cycle periodically between minimum (i.e., polishing composition flows into space between the wafer and pad) and maximum (i.e., polishing composition squeezed out, thereby allowing for the abrasive nature of the polishing pad to erode the wafer surface) values.
While current polishing pads have been suitable, there remains a need for an improved polishing pad. The invention provides such a polishing pad and a method of preparing and using such a polishing pad. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The inventive polishing pad comprises composite particles comprising a solid core encapsulated by a polymeric shell material, wherein the solid core comprises a material that differs from the polymeric shell material. The inventive method of polishing a substrate using such a polishing pad comprises providing a substrate and such a polishing pad, contacting the substrate with the polishing pad, and moving the polishing pad relative to the substrate to polish the substrate.